Laboratory Diagnosis of Rhabdomyolysis Definition of Rhabdomyolysis ‘Skeletal muscle injury, reversible or irreversible, that alters the integrity of the cell membrane sufficiently to allow the escape of cell contents into the extracellular fluid, and leakage into the cell of water, Na+, Cl-, and Ca++. Skeletal muscle is the largest organ in the body 40% of body weight Potential for extracellular fluid loss is large Potential for K+, PO4- -, enzymes, proteins, purine release is large ...